1. Field of the Invention
This invention relates to an information recording and/or reproducing apparatus and more particularly to an apparatus arranged to selectively record or reproduce information signals of different kinds.
2. Description of the Prior Art
High density recording has recently become a subject of pursuit in the field of magnetic recording. Video tape recorders (hereinafter referred to as VTR's) also have become capable of performing magnetic recording to a higher degree of density with the travelling speed of the tape lowered. Therefore, the conventional arrangement of using a fixed head for audio signal recording does not give a sufficiently high relative speed and thus results in the degradation of reproduced sound quality. In one of the solutions of this problem, the recording tracks formed by a rotary head are lengthened to have audio signals which are compressed on the time base recorded in the lengthened portion of the recording tracks one after another.
In the case of a VTR of the two-rotary-head helical scanning type, for example, a magnetic recording tape has been arranged to be lapped at least 180 degrees around a rotary cylinder. Then, a VTR of this type has been contrived, according to the above-stated solution, wherein the magnetic recording tape is lapped at least (180+.theta.) degrees around the rotary cylinder; and time base compressed audio signals which are pulse code modulated are recorded in the additional portion of .theta. degree. FIG. 1 of the accompanying drawings schematically shows the tape transport system of the above-stated VTR. FIG. 2 shows recording tracks formed on a magnetic tape by the VTR of FIG. 1. The illustration includes a magnetic tape 1; a rotary cylinder 2; heads 3 and 4 which are mounted with a phase difference of 180 degrees on the cylinder 2 and have different azimuth angles from each other; video signal recording areas 5 formed on the tape 1; and audio signal recording areas 6 formed also on the tape 1. Each of the video areas 5 is formed with the 180 degree lapped portion of the tape 1 on the rotary cylinder 2 traced by the heads 3 and 4. Each of the audio areas 6 is formed with the angle .theta. degree portion of the tape lapped on the cylinder 2 traced by the heads 3 and 4. In FIG. 2, reference symbols f1 to f4 represent the frequency values of tracking pilot signals superimposed on the recording tracks in accordance with a known four frequency method. The frequency values of these pilot signals are in the following relation: f2-f1=f3-f4.apprxeq.fH and f4-f2.apprxeq.2fH, wherein fH represents the horizontal scanning frequency of the video signal.
With the audio signal which is compressed on the time base and is pulse code modulated (hereinafter referred to as PCM processed) recorded in the audio areas, the audio signal can be reproduced with a high sound quality, which is comparable with the quality attainable by an audio apparatus which is adapted specially for recording and reproduction of an analog signal.
Meanwhile, there has been proposed a method of recording additional audio signals also in the video areas 5 of the VTR of the above-stated type. This method is as follows: Assuming that the angle .theta. is arranged to be .theta.=36, five additional audio areas are obtainable with the rotary head roated 180 degrees. Then, an arrangement to have time-base compressed audio signals recorded independently in these areas enables audio signals to be recorded in six channels. Thus, an audio dedicated or appropriated tape recorder can be arranged to be capable of recording audio signals in six channels. The following briefly describes this tape recorder:
FIG. 3 shows the tape transport system of the above-stated tape recorder. FIG. 4 shows recording tracks formed on a tape by this tape recorder. The same reference numerals and symbols are used as in FIGS. 1 and 2. While the head 3 or 4 traces distances from a point A to a point B, from the point B to a point C, from the point C to a point D, from the point D to a point E, from the point E to a point F and from the point F to another point G, audio signals can be recorded in areas CH1 to CH6. These areas CH1 to CH6 thus can be used for recording different audio signals therein respectively. An operation called azimuth-overwrite is performed on these areas. However, the tracks of these are CH1-CH6 do not have to be on the same straight line. Each of the areas CH1-CH6 has one pilot signal recorded therein for tracking control. Different pilot signals are thus recorded in different areas in the order of rotation f1.fwdarw.f2.fwdarw.f3.fwdarw.f4. However, there is no correlation between them.
Referring further to FIG. 3, recording or reproduction is carried out in or from these areas CH1 to CH3 while the tape 1 is travelling at a predetermine speed in the direction of arrow 7 and in or from the areas CH4 to CH6 while the tape is travelling in the direction of arrow 9. Therefore, as shown in FIG. 4, the inclination of the areas CH1 to CH3 somewhat differs from that of the areas CH4 to CH6. With regard to a difference in the relative speed of the tape and the head for these groups of areas, a difference arising from the travel of the tape 1 is extemely small as compared with a difference arising from the rotation of the heads 3 and 4. Therefore, the difference in the relative speed presents no problem.
FIGS. 5(a) to 5(j) show in a time chart the recording or reproducing operation of the tape recorder which is arranged as described above. A phase detection pulse (hereinafter referred to as a PG signal) which is generated in synchronism with the rotation of the cylinder 2 as shown at FIG. 5(a). The PG signal is of a rectangular wave of 30 Hz repeating a high level (hereinafter referred to as an H level) and allow level (hereinafter referred to as an L level) alternately with each other at intervals of 1/60 sec. Another PG signal which is of the opposite polarity to the PG signal of FIG. 5(a) is shown in FIG. 5(b). The first PG signal is at an H level while the head 3 is rotating from the point B to the point G of FIG. 3. The other PG signal shown in FIG. 5(b) is at an H level while the other head 4 is rotating from the point B to the point G.
Pulses for reading data are obtained from the PG signal of FIG. 5(a) as shown in FIG. 5(c). The data reading pulses are used for sampling the audio signal of a period corresponding to one field (1/60 sec). FIG. 5(d) shows by H level parts thereof periods provided for signal processing on the one field portion of the sampled audio data by adding an error correcting redundant code or by changing the arrangement thereof by means of a RAM or the like. FIG. 5(e) shows a signal indicating data recording periods at H level parts thereof which represent timing for recording, on the tape 1, the recording data obtained through the signal processing operation mentioned above.
Referring to FIGS. 5(a) to 5(j), the temporal flow of signals are, for example, as follows: The data sampled during a period from a point of time t1 to a point of time t3, i.e. while the head 3 is moving from the point B to the point G, is subjected to a signal processing operation during a period from the point of time t3 to a point of time t5, i.e. while the head 3 is moving from the point G to the point A and are then recorded during a period from the point of time t5 to a point of time 56, or while the head 3 is moving from the point A to the point B. In other words, the data is recorded by the head 3 in the area CH1 as shown in FIG. 4. Meanwhile, the data which is sampled while the PG signal of FIG. 5(b) is at an H level is also processed at a similar timing before it is recorded in the area CH1 by the head 4.
FIG. 5(f) shows another PG signal which is obtained by shifting the phase of the PG signal of FIG. 5(a) to a predetermined degree, which corresponds to one area and is 36 degrees in this specific instance.
An audio signal recording operation using the PG signal of FIG. 5(f) and a PG signal which is not shown but is of an opposite polarity to the former is performed in the following manner: The data which is sampled during a period between the points of time t2 and t4 is subjected to a signal processing operation during a period between the points of time t4 and t6 in accordance with the signal of FIG. 5(g) and is recorded during a period between the points of time t6 and t7 in accordance with the signal of FIG. 5(h). In other words, the data is recorded in the area CH2 of FIG. 4 while the head is moving from the point B to the point C. Meanwhile, another data which is sampled during the points of time t4 and t7 is likewise recorded in the area CH2 by means of the other head during a period between the points of time t4 and t7.
The signal which is recorded in the area CH2 in the manner as described above is reproduced in the following manner:
The head 3 reads the data from the tape 1 in accordance with a signal shown in FIG. 5(h) during the period between the points of time t6 and t7 (and also during the period between the points of time t1 and t2). Then, during the period between the points of time t7 and t8 also (between t2 and t3), the reproduced signal is subjected to a signal processing operation which is carried out, in a manner reverse to the signal processing operation performed for recording, in accordance with a signal shown in FIG. 5(i). In other words, error correction and other processes are carried out during this period. Then, during a period between points of time t8 and t9, the reproduced audio signal which has been thus processed is produced in accordance with a signal shown in FIG. 5(j). The reproducing operation of the head 4 is of course performed with a phase difference of 180 degrees from the above-stated reproduction by the head 3, so that a continuous reproduced audio signal can be obtained.
For other areas CH3 to CH6, it goes without saying that the recording and reproducing operation are performed on the basis of the PG signal of FIG. 5(a) by phase shifting it as much as n.times.36 degrees. This is independent of the travelling direction of the tape.
The prior art arrangement described above thus permits use of a VTR as an apparatus of multiple channel arrangement adapted solely for audio signal recording and/or reproduction.
The apparatus which is arranged as described above is capable of recording the audio signal over an extemely long period of time. However, an inaccurate grasp of the recording condition would increase the probability of an erroneous operation. In other words, there are recorded and unrecorded parts of the audio signal in each of the channels. Besides, a video signal might be recorded in the areas CH2 to CH6. In some cases, some part of a video signal might be left unerased. These things make it difficult to accurately grasp the actual record condition. If a video signal is erroneously recorded on the recording medium which is in such a condition, all the audio signals that have been recorded in the areas CH2 to CH5 might be completely erased. Further, if an audio signal happens to be recorded in any of the areas CH2 to CH5 of a recording medium on which a video signal has been recorded, the video signal would be nullified by the audio signal recording.